1. Field of the Invention
The present invention relates to the field of combustion engineering. The invention concerns a nozzle closing valve, particularly for a pressure atomizer nozzle of an oil burner, having an inlet side with an inlet passage, an outlet side with an outlet passage, a valve seat located between the inlet passage and the outlet passage, and a shutoff member. The shutoff member is pressed by means of a first spring located behind the shutoff member in a sealing member onto the valve seat and lifts from the valve seat counter to the force of the first spring when a predetermined pressure is reached in the inlet passage.
The present invention also relates to a pressure atomizer nozzle for an oil burner having a nozzle casing, which surrounds an inner space in the form of a blind hole. The inner space is connected in the base region of the blind hole by a nozzle bore to the outer space.
2. Discussion of the Background
A related nozzle closing valve and pressure atomizer nozzle are, e.g., illustrated in applicant's DE-Al-33 08 153 document.
In oil operated heating installations, in which the heating oil to be burnt is injected under a pressure of several (approximately 5) bar by a pressure atomizer nozzle into the combustion chamber, if no special pre-cautions are taken, on switching off the burner there can be a jet-like discharge or dripping of oil out of the pressure atomizer nozzle. In the shutdown phase and subsequent starting phase, such dripping leads to an excess of heating oil in the combustion chamber, which is rendered noticeable in the form of unburnt hydrocarbons in the flue gas and significantly deteriorates the emission values of the heating installation. The same undesired effects occur if, due to a heating of the oil in the feed line to the nozzle, there is a volume expansion leading to a pressure build-up in the line and to a discharge of oil from the nozzle opening.
Thus, in the aforementioned document it has already been proposed to equip the pressure atomizer nozzle of a heating installation with an automatically switchable shutoff valve. Such a shutoff valve, which operates with a resiliently pretensioned ball as the shutoff device and which is directly inserted in the nozzle, in the case of a significant pressure drop such as occurs on switching off, in the oil supply line stops the direct oil flow to the nozzle, so that the oil volumes present in the supply line between the solenoid valve and the nozzle can no longer pass out of the nozzle following switching off
In the related shutoff valve the valve ball, which rests directly on a metal valve seat, is pretensioned by a membrane-like elastic spring, which can spring backwards and forwards between two end positions and therefore has an extreme nonlinear characteristic. Through the use of the elastic spring it is ensured that the valve opens, e.g., at an opening pressure of 7 to 9 bar, but only closes again at a closing pressure of normally 4 bar. This hysteresis in the valve behavior has the advantage that, if the opening pressure on starting up the oil pump is once briefly reached and the valve opens, subsequently during a much lower operating pressure injection can take place, so that the oil pump efficiency is significantly improved.
However, it is problematical in the case of such a related valve that in practice it is extremely difficult to manufacture an elastic spring with a precisely predetermined spring characteristic, particularly as the spring only has a diameter of a few millimeters. In addition, as a result of the cooperation between the metal valve ball and the metal valve seat it is difficult to achieve an adequate sealing of the valve.
In the case of a compressed air oil atomizer nozzle, a valve located in the nozzle has been proposed, in which the shutoff member is constituted by a membrane or diaphragm pretensioned by a linear coil spring (EP-Al-566 855). The coil spring is housed in a spring chamber, which is admittedly sealed on one side by the membrane, but on the other side is connected to the nozzle opening through a relief opening. Thus, during operation oil can penetrate the spring chamber and, as the spring chamber is positioned behind the valve, can pass out of the nozzle after switching off However, in practice little oil enters the spring chamber. This is linked with the fact that in the case of the compressed air oil atomizer nozzle of EP-Al-566 855, other than with the pressure atomizer nozzle operating without compressed air of DE-Al-33 08 153, as a result of the compressed air a suction action is produced in the vicinity of the nozzle opening, which possibly immediately sucks off the oil entering th e spring chamber.
In order to solve these problems in an earlier-dated, not previously published application, namely European patent application 96810122.0, the applicant has already proposed a pressure atomizer nozzle with a nozzle closing valve, as shown in embodiments according to FIGS. 1 and 2. The pressure atomizer nozzle 1 according to FIG. 1 essentially comprises a nozzle casing 2 with a blind hole-like inner space 6. The nozzle casing 2 is flattened on the outlet side with a nozzle face 3, in whose center is located a nozzle bore 4. The nozzle bore 4 from which the oil flows out with a pressure of several bar, connects the inner space 6 of the nozzle 1 to the outer space. In the inner space 6 is placed a cylindrical conical insert 8, which is adapted with its conical tip to the hollow conical base of the inner space 6. Below the conical tip the external diameter of the conical insert 8 is reduced to a narrow, circular, circumferential bead 9, whose external diameter is adapted to the internal diameter of the inner space 6 and assumes the function of a type of filter in order to ensure that chips and the like do not reach the nozzle opening. As a result of the reduced diameter, between the conical insert 8 and the wall of the inner space 6, in the front part of the nozzle a circular overflow chamber 17 is formed. The overflow chamber 17 is connected to the nozzle bore 4 by helical grooves 12 made on the conical tip of the conical insert 8.
In the interior of the conical insert 8 is a blind hole 10, which extends from the rear (right-hand) end into the vicinity of the conical tip and is connected by one or more outlet passages 11 to the overflow chamber 17. The conical insert 8 carries on the rear (right-hand) end an external thread 13 by means of which it can be screwed into a corresponding internal thread 7 in the inner space 6. A nozzle closing valve 14 is positioned upstream of the conical insert 8 in the flow direction. The nozzle closing valve 14 shown in side view is also screwed by means of an external thread 30 into the nozzle casing 2 and is sealed by an O-ring 15 against the casing 2. On the inlet side the nozzle closing valve 14 is connected to a filter 16, which is preferably made from sintered metal. The nozzle closing valve 14 projects with a pin-like extension into the blind hole 10 of the conical insert 8. The pressure atomizer nozzle 1 with the screwed in nozzle closing valve 14 can in turn be screwed by means of an external thread 5 into a not shown oil preheater or the like.
In operation, the oil, which enters on the right-hand side through the filter 16 into the nozzle closing valve 14 is allowed to pass into the inner space 6 through a not shown outlet (f.24 in FIG. 2) not shown in FIG. 1, in the area behind the screw-in-thread with the valve open. It flows from there in the direction of the arrows through the outlet passages 11 into the overflow chamber 17 and from there via the helical grooves 12 into the nozzle bore 4, from where it is discharged in the form of an atomizing cone (shown in broken line form) into the outer space (combustion chamber).
The internal construction of the nozzle closing valve 14 of FIG. 1 is shown in longitudinal section in FIG. 2. The nozzle closing valve 14 is assembled from substantially rotationally symmetrical components 16, 18, 19, 20, 22, 23 arranged concentrically to a valve axis 32. The components inter alia comprise a cylindrical ring-shaped valve casing 19, which is terminated on one side by the fixed fitted filter 16. In the valve casing 19 is inserted an inner part 20, which contains an inlet passage 27 in the form of a concentric through-hole. The inner part 20 is supported on the inlet side on the filter 16 and on the outlet side is equipped with a valve seat 28, which surrounds in annular manner the outlet of the inlet passage 27. Into the valve casing 19 is also screwed a valve screw 18, which contains a spring chamber 29, a membrane seat 31 connected thereto and an outlet 24 projecting laterally upstream of the membrane seat 31 and fixes in the screwed in state the inner part 20 in the valve casing 19. As mentioned hereinbefore, the valve casing 19 has an external thread 30 with which it can be screwed into the pressure atomizer nozzle 1.
The shutoff member of the nozzle closing valve 14 is constructed as a diaphragm or membrane 23. The elastic membrane 23, which is inserted in the membrane seat 31, is sealingly pressed onto the valve seat 28 by a first spring 21 positioned behind the membrane 23. Counter to the force of the first spring 21 it only rises from the valve seat 28 when a predetermined pressure, i.e. the opening pressure, is reached in the inlet passage 27. The first spring 21 is preferably constructed as a coil spring and has a substantially linear spring characteristic. The first spring 21 acts on a thrust bolt 22, which in turn exerts pressure on the membrane 23 with a convex face.
The first spring 21 is housed in the spring chamber 29, which is constructed as a space (blind hole) open on one side and whose sole opening is sealingly closed by the membrane 23. The spring chamber 29 contains a compressible medium, which on opening the valve can be slightly compressed by the deforming membrane 23. As a result of its sealed nature no oil can penetrate it during operation, so that it does not constitute a harmful volume with respect to dripping. The rear marginal area of the membrane 23 rests on the membrane seat and is pressed by means of a second spring 25, also preferably a coil spring, against the membrane seat 31. This ensures that the membrane 23 always sealingly rests on the membrane seat 31. The second spring 25 is housed in an annular hollow space, which is formed between the front (left-hand) portion of the inner part 20 and the rear (right-hand) portion of the valve screw 18.
Laterally upstream of the membrane 23 in the flow direction an outlet 24 passes out of the valve screw 18 and at the front passes out of the valve casing 19. The inner part 20 is sealed against the valve casing 19 with a further O-ring 26. Coming from the right-hand side, the oil passes through the filter 16 into the inlet passage 27 and from there presses in the membrane 23, namely on a surface bordered by the valve seat 28. With rising pressure the membrane 23 bends to the left and presses the thrust bolt 22 to the left and compresses the first spring 21. On reaching the opening pressure of, e.g., 5 to 7 bar, the membrane 23 lifts from the valve seat 28, so that the oil can fill the space of the second spring 25. The oil now presses on a larger surface, bordered by the membrane seat 31, onto the membrane, so that a lower pressure is adequate in order to compensate the same spring force of the first spring 21. Therefore the oil pressure keeping open the valve closing valve 14 is much lower than the opening pressure. With the membrane 23 raised, the oil then flows out of the outlet 24 into the inner space 6 of the pressure atomizer nozzle 1, as described hereinbefore.
Preferably, between the membrane 23 and the second spring 25 is provided a metal collar 33, which uniformly distributes the pressure of the second spring 25 onto the edge of the membrane 23 and therefore improves the seating of the membrane 23 in the valve and the sealing action relative to the spring chamber 29. Preferably, the thrust bolt 22 has a diameter-enlarged, convexly rounded head, which on compressing the thrust bolt 22 in the opening direction of the valve rests on a step formed in the valve screw 18 and therefore limits the displacement path of the thrust bolt 22, i.e. the valve clearance.
The pressure atomizer nozzle with nozzle closing valve according to the prior application and FIGS. 1 and 2, as a result of its construction, leads to significant advantages compared with the related art. However, the range of use of the nozzle closing valve 14 is limited by the fact that the valve with the part of the valve screw 18 projecting out of the valve casing 19 penetrates far into the blind hole 1 of the conical insert 8. Thus, the valve requires additional space, which leads to corresponding limitations with respect to the design of the conical insert 8.